The present invention relates to a method for producing a connector element for connecting frame parts at a joint location in a bicycle framework, and a connector element obtained thereby. The invention is further particularly related to a bicycle bottom bracket obtained by this method.
The Applicant has recently conducted various studies and tests to make bicycle components, such as wheel hubs or bottom brackets for housing the bicycle crank axle, using structural fibre based material, typically carbon fibre based material. The advantage offered by this type of material is that of being light in weight with respect to the metal materials used in the past, given equal structural characteristics. However, making a component of the above indicated type out of a single part of carbon fibre based material proved to be very difficult heretofore, due to the complex conformation of such components.
The object of this invention is to overcome this technical problem.
In order to attain this object, the present invention provides a method for producing a connector element for connecting frame parts at a joint location in a bicycle framework, characterized in that it comprises the following steps:
arranging an expandable core,
applying a number of layers of structural fibre fabric incorporated in a plastic material matrix around the core, to form a layered body, of predetermined shape and thickness,
arranging the core with the layered body in the cavity of a mould,
increasing the temperature of the mould (21) to a value sufficient to cause the reticulation of the plastic material matrix,
expanding the core so as to apply a pressure on the body inside the mould,
removing the body from the mould and removing the core from the body, so as to obtain a hollow body formed of a single piece of structural fibre based material.
Further features of the method of the invention are defined in the appended claims.
Structural fibre fabrics incorporated in a plastic material matrix are known and have been used for some time. They are made with yarn obtained from structural fibres, such as carbon fibres, for example. These fabrics are then subjected to a calendering process to associate them to a plastic material matrix, typically a thermosetting plastic material.
In the preferred embodiment of the method according to this invention which is defined in claims 9-19, a plurality of fabric layers of this type are wrapped around a core defined by a metal body with a sheath of expandable plastic material, the conformation of which correspond to that of the body to be obtained. In this way, when the mould is heated to reticulate the thermosetting matrix of the layered tubular body wrapped around the core, the material forming the sheath dilates whereby it applies a radial pressure on the walls of the hollow body, which is beneficial to obtain a product with the necessary structural characteristics. The fundamental advantage of the thermally dilating sheath is that of allowing the uniform application of such pressure, despite the possibly complex conformation of the pre-formed body.
In the preferred embodiment of this invention, said structural fibres are carbon fibres and the plastic material matrix is a thermosetting plastic material matrix. The temperature to which the mould must be taken in order to complete the process is preferably comprised in the range from 80xc2x0 C. to 200xc2x0 C. The mould is preferably maintained at a temperature in this range for a time comprised in the range from 10 minutes to three hours, preferably from 30 minutes to three hours from 30 minutes to three hours.
This invention also relates to a connector element for connecting frame parts at a joint location in a bicycle framework, which is obtained with the method of the invention. In the preferred embodiment, the method of the invention is used to obtain a bicycle bottom bracket, which is the part of the bicycle frame for housing the bicycle crank axle, with integrated tubular extensions for connecting the down tube and the seat tube of the bicycle frames which converge into the bottom bracket.
However, the invention may be also applied for obtaining a connector element to be used at any other different location of the bicycle frame where two or more frame parts converge into each other, such as at the intersections of the frame head tube with the top tube and the down tube or at the intersections of the seat tube with the top tube or the elements of the bicycle upper rear fork.
According to another aspect, the invention is also directed to a connector element for connecting frame parts at a joint location in a bicycle framework, characterized in that it consists of a single piece made of structural fibre based material, preferably carbon fibre material, incorporating a main tubular portion and one or more tubular branches departing from the main portion, which are to be connected to tubular elements of the bicycle frame.
As indicated above, the connector element of the invention is here shown in form of a bicycle bottom bracket, but can also be made in form of a connector element for any other joint location of the bicycle frame.
Naturally, once the method is completed, the body thus obtained can be subjected to additional machining, to make a finished product ready for use.